Glacier melt rate a surprise [Southeast Alaska]

Glacier melt rate a surprise Ice in Southeast vanishing twice as fast as expected The glaciers of Southeast Alaska are shrinking twice as quickly as scientists

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, Aug 4 11:47 AM

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Glacier melt rate a surprise

Ice in Southeast vanishing twice as fast as expected

The glaciers of Southeast Alaska are shrinking twice as quickly as
scientists had previously estimated, according to a new study.
The findings from Fairbanks and Juneau glaciologists are slated for
publication in a leading scientific journal.

During a 52-year period, the Panhandle lost ice in 95 percent of its
glacier-covered areas, said Roman Motyka, of Juneau, one of the
study's co-authors.

The scientists participating in the study pinpointed the amount of
ice loss by analyzing changes in the elevation of Southeast Alaska's
glaciers between 1948 and 2000.

Their measurements show Southeast Alaska lost an average of roughly
14.6 cubic kilometers of ice per year during that time period.

A cubic kilometer roughly equates to 264 billion gallons of water -
about a quarter more than Los Angeles consumes in one year, according
to estimates by NASA.

"It's a pretty substantial loss of ice," Motyka said, noting the
melting of Panhandle glaciers raised global sea levels by roughly
0.04 millimeters per year. In all of the years combined, Panhandle
ice loss caused the world's oceans to rise roughly 2.4 millimeters,
according to the study.

Scientists involved in the study said this week the Panhandle's ice
reservoirs have retreated more drastically during the past couple of
years.

The study's lead author, Chris Larsen, also of the Geophysical
Institute, plans further measurements this month at Panhandle
glaciers, ranging from Petersburg's Stikine Icefield to the St. Elias
Mountain Range.

Scientists aren't the only ones noticing the wastage of most of the
Panhandle's glaciers.

Juneau residents and tourists visit the retreating Mendenhall Glacier
daily. Some of the most dramatic ice losses in the Panhandle are
underway at lake-terminating glaciers, such as the Mendenhall, fed by
the Juneau Icefield, according to the study.

"I just few over the Juneau Icefield three days ago. I was absolutely
shocked by how dry and shrunken it looked," said Nick Jans, a Juneau
author, on Tuesday.

Further to the south, the amount of ice loss at Tracy Arm's South
Sawyer Glacier is "not even conceivable," said Juneau photographer
Mark Kelley.

Kelley has photographed the glacier for the past 25 years and
recently collaborated with Jans on a 40-page book about Tracy Arm's
glaciers. In 2004, the South Sawyer Glacier retreated approximately
one-half mile, clogging the water with icebergs.

"Just think about that volume. The glacier was 1,100 feet thick and a
mile across," Kelley said.

Motyka is concerned a runaway process - initially triggered by
climate warming but now controlled by glacial calving dynamics - may
already be underway in Southeast Alaska.

More of the same could be in store for world's other coastal
glaciers, he said.

"We have a lot of ice (in Southeast Alaska), but Greenland has more,"
Motyka said.

In Greenland, Motyka and other Geophysical Institute scientists are
attempting to learn how dramatic loss of ice at the base of a large
tidewater glacier, the Jakobshavn, is affecting the ice sheet at the
top.

"I worry that these (tidewater) glaciers will bring down the ice
sheet, no matter what happens with climate," Motyka said.

"If Greenland goes unstable, a lot more water will be going into the
ocean. This could cause problems with ocean currents," Motyka
explained.

The Panhandle study - now under review by third-party scientists - is
the first to measure ice loss at all major Panhandle glaciers.

A previous study, published in 2002, profiled ice loss at 12 glaciers
in Southeast Alaska. When those results were extrapolated to the rest
of the Panhandle, the result was a significant underestimate of
regional ice loss, Motyka said.

The new study was enabled by a 2000 NASA Endeavour space shuttle
project called the Shuttle Radar Topographic Mission. Among other
duties, the shuttle mission produced a new three-dimensional radar
map of Southeast Alaska.

Motyka and his colleagues collected the NASA maps and compared them
to topographical maps and high-resolution photographs of Southeast
Alaska dating back to 1948.

After final revision, a paper describing the Panhandle study will be
published in the Journal of Geophysical Research.